spring

• tenets of Spring boot

  • dependency management
  • auto-configuration
  • simple deployment - I know k8 and docker, heh

• main annotations

  • [[@SpringBootApplication]]
  • [[@Component]]

• [[REST]] is the way stuff works now

• #spring bean - is something that's created by Spring and its lifecycle is managed from within the Spring framework - user never specifies it's creation or GC #confirm

• wow you can create an api by just doing this

@RestController
class ProductService {
    private List<Product> products = new ArrayList<Product>();
    public ProductService() {
        products.addAll(List.of(
            new Product("1", "potato"),
            new Product("2", "onions"),
            new Product("3", "chips"),
            new Product("4", "fruits")
        ));
    }

    @GetMapping(value = "/products")
    Iterable<Product> getProducts() {
        return products;
    }
}

• you can use Optional<type> as the return param for an api if the value can be empty

@GetMapping(value = "/products/{id}")
    Optional<Product> getProductById(@PathVariable String id) {
        for(Product p: products) {
            if(p.getId() == id) return Optional.of(p);
        }

        return Optional.empty();
    }

• java == operator tries to equate the references instead of the values - yikes
• use .equals() method to check on values
• [data-access]
• [[@Autowired]] is not needed if there's a single constructor
• to do run some code at the start of application start you can do by three ways
  • annotate a class with [[@Component]] and create a method with @PostConstruct simple
  • use [[CommandLineRunner]]
  • or use [[ApplicationRunner]]

configuration

ways we can environmentify the application

application.properties

• by default is present in the maven flavoured codebase
• can be used using @Value with some expression language to get the value

an example showing reading value from application.properties

@RestController
class ConfigParamsController {
  @Value("${environment}")
  private String environment;

  @GetMapping("/environment")
  String getEnvironment() {
    return environment;
  }
}

@ConfigurationProperties